Christian Munzinger

Simulation and optimization of complete mechanical behaviour of machine tools

Up to now the consideration of forces between flexible, moved structures, e.g., linear guides on base frame components, depending on different workspace positions wasn’t possible in multi-body simulation. Thereby neither the representation of the complete mechanical behavior nor the optimization of the frame structure depending on different workspace positions is possible. In the context of the Priority Program 1099 of the German Research Foundation “Production Machines with Parallel Kinematics”, methods have been developed, which enable the transmission of forces between flexible bodies multi-body simulation. The existing, flexible MBS-model of the coupler kinematics “Genius 500” is extended by a flexible frame structure and the total deformation is analyzed. Furthermore the present frame structure is replaced by a design space for topology optimization in different workspace positions.

An approach for compensation of geometric faults in machine tools

Geometric faults in parts of machine tools with parallel kinematics lead to stresses in the structure and deflections of the tool center point, reducing the quality of the workpiece. Improving the design of machine tools can reduce these influences. In this paper an approach to compensate the influence of geometric faults in parallel kinematics based on the design of an adaptronic strut is introduced. The strut is divided in two halves and two piezoelectric transducers are implemented in between them, used as sensor and actuator, respectively. A preliminary design of the adaptronic strut is presented. The problems of measuring low-frequency signals using piezoelectric transducers are considered in the design. Finally, a primary analytical model of the dynamical behavior of the adaptronic compensation unit is presented. The strut and its connection to the surroundings are regarded as a flexible multibody system, the equations of motion are derived using linear graph theory. Some simulation results are presented.Copyright

Adaptronical compensation of geometrical machine errors

Static, quasi-static and dynamic displacements influence the accuracy of machine tool results. The low-frequency parts of these displacements can, on the one hand, be traced back to static stresses resulting from gravity as well as process loads and, on the other hand, to geometrical machine errors and the faulty positioning in the working area resulting from this. Dynamic loads, however, are characterised by the distribution of masses and stiffnesses. This paper aims to present an approach to adaptronically compensate for static and quasi-static displacements while, at the same time, showing how a component can fulfill the functions of a sensor and an actuator. In order to achieve this, an intelligent adaptronical strut was designed for which the piezoelectric transducer can fulfill actuated as well as sensoric tasks at the same time. Based on the principle of vibrating strings, a vibrating string is used to induce vibrations which allow for the static, quasi-static and dynamic machine displacements to be recorded using the developed integrated sensors and actuators. A first prototype was integrated into a machine tool to verify the concept. Static and dynamic measurements endorse the functionality of this approach. Machining trial runs show the effectiveness of this approach in a parallel kinematic machine tool with regards to adaptronically compensating for geometrical machine errors.

Component-specific scale for inline quality assurance of spatially curved extrusion profiles

Spatially curved Al-extrusion profiles are often used for lightweight frame structures in vehicle manufacturing. Within the Collaborative Research Centre SFB/Transregio 10, an automated product-flexible process chain is established in order to produce and machine such profiles and to join them into frame structures. One of the biggest challenges of this process chain consists in handling, clamping and machining variably formed profiles with precision and without having to change the mechanical system. For this, both the contour of the profile and the position and orientation of the profile during the process have to be determined. In order to have this information provided from inside the process chain, a component-specific scale was developed and realised for the contour detection and precision positioning of multi-dimensionally curved extrusion profiles. The scale is applied onto the surface of the profile by a laser. To determine the contour, the scale is scanned using digital image processing and the profile is measured by a laser triangulation sensor. This establishes the relation between component scale and profile contour. If required, the position of the profile can be readjusted by scanning individual markings again during machining. It is not necessary to re-measure the entire profile contour. The process can be used for different profile contours and profile lengths without having to change the mechanical system. The first section of this article describes the approach for contour detection and precision positioning and its validation for straight profiles, 2D curved profiles and 3D curved profiles with a test rig. Then, the implementation of the validated process into a process chain is described, including the inline application of the scale, the inline profile measuring and the precision positioning of spatially curved profiles during machining.

Flying Cutting of Spatially Curved Extrusion Profiles

The innovative process of curved profile extrusion facilitates the cost-effective production of lightweight structures with spatially curved profiles even for small series. Due to the extrusion process a continuous flow of material is unavoidable. The profiles have to be separated reactionlessly during the extrusion following the complex trajectory of the cut-off point in space. This paper discusses the challenges for a flying cut-off device. In addition to a concept to generate the trajectories and control the movements, the main parameters for dimensioning a cut-off device are presented. A specially designed clamping device permits to generate high accelerations. Further on, cutting results are shown especially for extruded sections with continuous reinforcing elements of steel.

Designing Adaptronical Components for Compensation of Static and Quasi-Static Loads

The increasing interest in active solutions for the compensation of static and quasi-static displacements at tooling machines, like mechatronics and adaptronics for example, must be looked at with regard to high dynamics and accuracy. Mechatronical systems for the compensation of displacements allow for high manufacturing accuracy and at the same time high machine dynamics. The high system costs make an application in industrial environments impossible. Besides mechatronics the area of adaptronics shows a high potential for cost reduction and system integration with a comparable functionality. This article describes the compensation for piezoelectric transducer stacks in the static and quasi-static range in particular. The piezoelectric transducers stand out for their excellent properties as actuators such as positioning accuracy and dynamics. The multifunctional properties of piezoelectric transducers allow for the spatial and functional integration of sensor and actuator for the realization of active components. Due to a limited time constant for the use of piezoelectric transducers as sensor, static loads must be transformed into a dynamic input signal for the transducer. The interdisciplinary design of the overall system is of vital importance. It is described and discussed by the example of the realization of an adaptronic strut with controllable elongation for parallel kinematics and an adaptronic hydrostatic pressure pocket unit for an intelligent hydrostatic leveling system.Copyright

Towards the flexible and near-net-shape production of three-dimensionally curved extrusion profiles

The present paper describes the new developments in continuous extrusion of curved profiles by a flexible production method which is composed of a short process chain starting with the extrusion press, a deflection tool, one robot for the flying cutting of the profile and another robot for supporting and handling the profile. Because of the flexibility of this complete system according to the profile curvature it is convenient for small-volume production. In order to reach high profile accuracy all kinematic systems in the process chain have to be synchronized with the profile speed caused by the extrusion process. The results of the investigation of different existing synchronization methods identify the need for an additional measuring system to compensate the large deviation of the cut profile length. By adjusting parameters of the synchronization the accuracy of the profile length could be strongly improved. Furthermore influencing parameters like die deformation during the extrusion process are measured and combined with the results of the cut profile length over the process time.

Piezoelectric control of a machine tool with parallel kinematics

An adaptronic strut, developed for compensation of the influence of geometric faults in machine tools with parallel kinematic structure, is examined. A simple oscillator model of the strut is built. First, the equations of motions for this simplified model are derived analytically. These information are used for designing a single variable state control based on the principles of the optimal least quadratic regulator (LQR). Afterwards, the controller concept is extended applying an additional PI-controller. Secondly, the strut is modeled using the commercial multi-body system simulation software Msc.Adams. The required system state which is not explicitly given within Msc.Adams primarily has to be estimated. For this task a Luenberger observer is implemented. A similar single variable state control is developed and both designs are compared among themselves when the adaptronic strut is examined under external loads. Finally, the strut is implemented into the model of the complete machine tool and its influence on the behavior of the machine tool is treated.

Efficient Simulation of Parallel Kinematic Machine Tools

Today’s machine tool industry mainly consists of small and medium-sized enterprises. Thus, the simulation of new products often does not seem to be cost effective due to the small number of items produced and the high cost of simulation tools. Nevertheless, the use of simulation tools is essential in order to tap the full potential of new challenging concepts like parallel kinematic machines. This paper presents a simulation method supporting the development process of parallel kinematic machine tools from the first concept to the prototype. In order to render the method applicable for the machine tool industry, a special focus is placed on tool efficiency. A modular modeling concept will ensure that the structure of the first kinematic model of the concept phase can be enhanced during the development process and developed into more detailed models, e.g. for dimensioning calculations or to study the dynamic behavior of machine tools. Thus, the method efficiently supports the whole development process with a simulation model gradually increasing in detail according to the requirements of the machine tool designer.Copyright

Accuracy of a Flying Cutting Device

The prototype for the flying cutting of spatially curved extrusion profiles developed as part of the Collaborative Research Center Transregio 10 (SFB/TR 10) was tested as an integrated part of the overall system in first test runs. The profiles resulting from this process give proof of the potential involved in both, the novel curved profile extrusion (CPE) and the automatic supporting and cutting device. For subsequent automated processing to become possible, however, the reliably achievable accuracy of extruded profiles needs to be further improved. By the example of the extruded profiles produced so far, this article discusses potential factors that may impair profile accuracy and presents approaches and methods for the improvement of accuracy.